Background Statement for SEMI Draft Document 5634

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Background Statement for SEMI Draft Document 5634

New Standard: TEST METHOD FOR COLOR REPRODUCTION AND PERCEPTUAL CONTRAST OF VISUAL DISPLAY

Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.

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Background

As high quality properties of digital TV like HDTV, 4K UHDTV and 8K UHDTV have been demanded, it is necessary to present the highest image quality with rich and authentic color, subtle gray and color tone and dynamic contrast, and set the suitable and advanced evaluation methods of display quality. The aim of various methods for measuring color gamut, brightness, and contrast based on human perception have been studied is to match the image quality with human eyes. Even though there are conventional measuring methods like luminance, tristimulus values for the objective evaluation method, there are imperfect methods considering a viewing condition, perceptual parameters. The basic rationale of this document is the color appearance model which is proposed at CIE in 2002. A new method is to calculate a color volume and contrast with color appearance model which is uniform color space with human visual perception.

Review and Adjudication Information

SEMI Draft Document 5634

New Standard: TEST METHOD FOR COLOR REPRODUCTION AND PERCEPTUAL CONTRAST OF VISUAL DISPLAY

1 Purpose

1.1 This standard specifies measurement conditions and methods for describing the visual color quality in 3-dimensional color space, and the perceived contrast with perceptual parameters in Organic Light Emitting Diode (OLED) displays.

1.2 The CIE XYZ color space is derived from the experimental results and it has been used to set color performance of displays in CIE xy or u’v’chromaticity diagram without brightness.

1.3 For measurement, setting test patterns based on Average Picture Level (APL) of IEC 62087:2011 are required, instead of full screen patterns, which are composed with small size of window box. The full screen patterns are not suitable for OLED displays which of luminance are adjusted with contents.

1.4 The contrast ratio has been widely used although the calculated value is dramatically changed by dark state luminance. This metric does not consider human visual characteristics.Therefore, it is more reliable to consider the perceptual indices.

2 Scope

2.1 This standard is applicable to the color OLED displays.

2.2 This standard includes the measurement for physical data, analysis, calculation methods with perceptual factors.

2.3 The term “perceptual” is subject to CIECAM02 (CIE Color Appearance Model 2002) in this standard.

NOTICE:This standard does not purport to address safety issues, if any, associated with its use. It is the responsibility of the users of this standard to establish appropriate safety and health practices and determine the applicability of regulatory or other limitations prior to use.

3 Limitation

3.1 Measurements are subject to errors or imprecision due to the user, environmental factors, and mis-calibration of measurement system or measurement system limitations.

3.2 Results may vary with ambient illumination conditions or in the presence of uncontrolled stray light reflections.

4 Referenced Standards and Documents

4.1 IDMS

4.1.1 Information Display Measurement Standard (IDMS)1.0

4.2 CIE Standards[1]

CIE 15.3 —Colorimetry

CIE 159 —CIECAM02

4.3 IEC Standards[2]

IEC 62341-6-2 — OLED Displays — Measuring methods of visual quality and ambient performance

IEC 62087— Methods of measurement for the power consumption of audio, video and related equipment.

NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 APL–average picture level.

5.1.2 PCL–perceptual contrast length

5.1.3 VCRC–volume color reproduction capability

5.2 Definitions

5.2.1 brightness–the attribute of a visual sensation according to which an area appears to emit more or less light

5.2.2 color gamut boundary–the outer surfacedetermined by a color gamut form

5.2.3 perceptual contrast length– the difference of black and white brightness on the same point of the screen

5.2.4 volume color reproduction capability –the volume of the perceived color gamut obtained in brightness color space which is composed of colorfulness, hue and brightness

6 Standard Measurement Condition

6.1 Measuring Conditions

6.1.1 Environmental conditions

6.1.1.1 In order to obtain accurate measured data, the following environmental conditions are required.

• Temperature: 25±2 °C
• Humidity:25-85% relative humidity
• Pressure: 86-106 kPa
• Air flow: no wind
• Vibration / Shock: no influence
• Ambient illumination conditions
• Dark room condition
• The luminance contribution from the background illumination shall be less than 0.01cd/m2.
• Ambient illumination conditions
• Uniform hemispherical diffuse light source
• Directed light source
• The type of light source used, and its Correlated Color Temperature (CCT), should be noted in the ambient performance report.This measurement with directed light source should be performed in a dark room which should be maintained with windowless and gray or black curtains and rugs.
• Measuring equipment conditions
• In this standard, a light measuring device such as spectroradiometer, at least the 380 nm to 780 nm wavelength rangeor a filter photometer shall be used.
• The photometric accuracy of the instrument shall be within±2 %.
• The standard measuring distance is 3H (for H≥20 cm) or 50 cm (for H<20 cm) where H is the height of the measured display device.
• Viewing Direction
• In the case of the uniform hemispherical diffuse illumination conditions, an integrating sphere, sampling sphere, or hemisphere shall be used.The configuration shall follow the standard di/8° to di/10° illumination/detection geometry, where di is the standard notation for diffuse. The basic viewing direction of this test is shown in Figure 1. However, for a specific case, other viewing directions, like perpendicular to the display can be used.

Figure 1
An example of measuring configuration with sampling sphere

7 Summary of Test Method

7.1 Test Patterns

7.1.1 A centered window box occupying 4% of the screen area is used. The 100% intensity (e.g., 255 gray level in 8bits) for window box and the 40% intensity (e.g., 102 gray level in 8bits) for background is applied. One of the test patterns is shown in Figure 2.

Figure 2
Test pattern of 4% window box with 40% gray background

7.1.2 Each of the following eight colors in the 4% window box at the center of the screen is applied.

• Red: (255, 0, 0)
• Green: (0, 255, 0)
• Blue: (0, 0, 255)
• Yellow: (255, 255, 0)
• Magenta: (255, 0, 255)
• Cyan: (0, 255, 255)
• Black: (0, 0, 0)
• White: (255, 255, 255)
• It may be necessary to use some kind of a mask or stray-light-elimination tube to avoid veiling glare in the detector when measuring 4% window box colors.
• The intensity of colors is based on 8 bits. However, for the other color bits, like 10 bits or 12 bits, the intensity of color should be changed.
• Measuring Set-up
• Electrical conditions, warm-up time and adequate integration time follow section 3.2 of IDMS 1.0 methods.

8 Procedure

8.1 The following measuring procedure is recommended for the measuring of tristimulus values of each of colors.

• Check and measure the conditions described in ¶¶ 6.1.1 and 6.1.2.
• Set the measured display and signal generator for the test patterns.
• Set the distance between display and LMD (Light Measurement Device).
• Install the angle of LMD against the display.
• Apply the eight test patterns at the display.
• Measure the luminance and chromaticityat the center of the window box with eight test patterns, respectively.
• Record the measurement data.
• Record the measurement conditions which are room conditions, aging conditions, and ambient conditions.

9 Calculations

9.1 Analysis Method for Color Reproduction

9.1.1 The 17 interpolated gradation points between black and the other six primary and secondary (RGBYMC) colors using gamma 2.2 should be calculated. The calculation method is described in Appendix 1.

9.1.2 The measured and interpolated data for all defined colors shall be transformed into the CIECAM02 3 dimensional color space, which is described in Appendix 1.

9.1.3 Color reproduction which is color gamut volume with brightness, colorfulness, and hue of the transformed data is calculated.

• Search the color boundary surface in 3-dimensional color space, which is determined by a color gamut’s extremes.

Figure 3
An example of color reproduction

• Set the smallest triangulation of surface points.

Figure 4
The geometry of trigonal pyramid of connecting points with an inside point

• Calculate the color volume of trigonal pyramid and add up all volume of trigonal pyramids.

where N = {1,2,3, …, MAX}

Color Volume(1)

9.2 Analysis Method for Perceptual Contrast

9.2.1 PCL is the length between black and white brightness. The calculation method for brightness is described in Appendix 1.

• Calculate the contrast length between black and white brightness.

PCL = white brightness – black brightness(2)

10 Report

10.1 The color reproduction named VCRC (Volume Color Reproduction Capability) in 3D color space is represented with percent relative to sRGB color volume in CIECAM02. An example result is shown in Table 1.

Table 1An example of a result report for the VCRC

10.2 For the PCL, there is a table of the result report which is shown in Table 2.

Table 2A worked Example of a result report for the Perceptual Contrast Length

APPENDIX 1COLOR SPACE CONVERSION METHOD

NOTICE: The material in this Appendix is an official part of SEMI [designation number] and was approved by full letter ballot procedures on [A&R approval date].

A1-1 CIECAM02 color model

A1-1.1 A color appearance model provides a viewing condition specific method for transforming tristimulus values to and from perceptual attribute correlations. The CIECAM02 is useful for color management applications. This model consists of a chromatic adaptation transform and equations for computing a set of perceptual attribute correlations. A set of perceptual attributes is only focused on dim condition for TV application. Also, brightness color space for color reproduction is used, instead of lightness color space of CIELAB or CIELUV. Brightness is defined by the CIE as the attribute of a visual sensation according to which an area appearsto emit more or less light.

A1-1.2 The normalized tristimulus values to a long, medium and shortwavelength sensitive space conversion

(2)

where;

(3)

A1-1.3 The degree of adaptation to the white point calculation

(4)

where;

• LA: one-fifth of the measured white luminance.

A1-1.4 The weighted chromatic adaptation with D factor calculation

(5)

where;

• RW, GW, and BW: the RGB values computed for the white point.

A1-1.5 The viewing condition dependent constants calculation

(6)

where;

• Yb: 20,
• Yw: 100

A1-1.6 Hunt-Pointer-Estevez space conversion for applying the post-adaptation non-linearcompression

(7)

where;

(8)

A1-1.7 Post-adaptation non-linear compression

(9)

A1-1.8 Temporary Cartesian representations and hue calculation

(10)

A1-1.9 The achromatic response calculation

(11)

A1-1.10 Lightness is calculated from the achromatic signals of A and AW

(12)

A1-1.11 Brightness calculation

(13)

A1-1.12 Temporary magnitude quantity, tcalculation

(14)

where;

(15)

A1-1.13 chroma, C calculation

(16)

A1-1.14 colorfulness, M calculation

(17)

A1-2 Color conversion

A1-2.1 Luminance of interpolated gradation points should be calculated, as follows:

(18)

where;

• LQmax: maximum luminance for a measured color Q
• LQmin:luminance of black
• Q: red, green, blue, cyan, magenta, yellow
• n = {0, 17, 33, 49, 65, 81, 97, 113, 129, 144, 160, 176, 192, 208, 224, 240, 255}

A1-2.2 Tristimulus values between black and the other six primary and secondary (RGBYMC), which is interpolated gradation points should be calculated with LQn.

(19)

where;

• Q: red, green, blue, cyan, magenta, yellow
• n = {0, 17, 33, 49, 65, 81, 97, 113, 129, 144, 160, 176, 192, 208, 224, 240, 255}

A1-2.3 The interpolated gradation points shall be transformed into the CIECAM02, which is described in A1-1.

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